An object of the present invention is a probe, provided with a concave arrangement of piezoelectric elements, for an ultrasound apparatus. A probe of this type can be used, in particular, in the medical field in association with an echograph type of apparatus. Nonetheless, it can find application in other fields where ultrasound is used and where, for needs of focusing, it is preferred to use probes provided with piezoelectric elements distributed on a concave surface.
A probe for an ultrasound apparatus comprises, in principle, several piezoelectric transducer elements to convert electrical signals applied to the elements into mechanical excitations and vice versa. These piezoelectric elements are arranged in the head of the probe according to a matrix type distribution, most often with two dimensions, sometimes with one dimension, for example in a bar. The making of a probe of this type, in the face of the need to supply, electrically and independently, each of the elements is not a simple problem. A solution, in principle, consists in fixing, to a metallized, flexible support, a plate of a piezoelectric crystal, and in making cuts in this plate without excessively penetrating the support. In this way, the desired distribution of the elements is obtained. In having made sufficiently wide cuts and in curving the elastic support, a desired concave shape can be imposed on it. In doing so, the electrical supply of the two faces of the piezoelectric elements is not easily resolved. In effect, since the useful acoustic transmission is propagated on the side of the concavity, it is inappropriate to make independent connection circuits on this surface. This is all the more troublesome as, for reasons of acoustic propagation, it is necessary to place, on top of each of the elements, an acoustic transmission blade with a thickness substantially equal to a quarter of the wavelength of the wave, which goes through it at the working frequency of the probe. This problem of connection is a major brake on the development of probes, especially those for which the piezoelectric arrangement is two-dimensional.
The characteristics of a concave ultrasound probe are known from the Japanese abstract 57181299. The support 1 known from this document is thermodeformable and the acoustic transition blade is cut up by saw marks. The joining of elements 3 to a plate 4 is known from the Japanese abstract 60249500. This plate is not described as being an acoustic transition blade.
An object of the present invention is to overcome these drawbacks in observing that, for the applications sought, with a focusing imposed by the curvature of the arrangement of the elements, it is not troublesome for the tips of elements covered with their transition blade to touch one another in the concavity of the probe. In the invention, the idea was then had of reversing the problem and using a common transition blade, continuously metallized throughout its surface, and to which all the piezoelectric elements are fixed. The result thereof is that the electrical connection for the differentiation of all the elements can be done through the rear of the probe, where there was previously the support. These electrical connection circuits disturb the rear wave of the probe, which is of no importance. They do not hamper the useful operation of the probe. The concave arrangements of piezoelectric elements are obtained by using flexible blades which may possibly be thermodeformable. The metallizations of the front and rear faces enable the application of an electrical field parallel to the direction of propagation of the sound waves. This arrangement is advantageous because it improves the coupling coefficient between the electrical field and the acoustic field.
The piezoelectric elements comprise, for example, plastic elements such as PVF.sub.2 or copolymer PVT.sub.2 F: a ceramic such as PZT for example, the polymer compound PZT or the PBTiO.sub.3 or a crystal.
An object of the invention, therefore, is a probe for ultrasound apparatuses provided with a concave arrangement of piezoelectric elements, said elements being each covered, on their emitting face, in front of the concavity, with an acoustic transition blade, characterized in that adjacent blades form one and the same continuous integral blade covering several elements.